Currently, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium secondary batteries, and the like are used as commercial secondary batteries. Among them, lithium secondary batteries have little to no memory effect in comparison with nickel-based secondary batteries, and thus lithium secondary batteries are gaining a lot of attention for their advantages of free charging or discharging, low self-discharging, and high energy density.
A lithium secondary battery generally uses lithium oxide and carbonaceous material as a positive electrode active material and negative electrode active material, respectively. The lithium secondary battery includes an electrode assembly in which a positive electrode plate and an negative electrode plate respectively coated with the positive electrode active material and the negative electrode active material are disposed with a separator being interposed between them, and an exterior, namely a battery case, which seals and accommodates the electrode assembly together with an electrolyte.
Generally, a lithium secondary battery may be classified into a can type secondary battery where the electrode assembly is included in a metal can and a pouch type battery where the electrode assembly is included in a pouch of an aluminum laminate sheet, depending on the shape of the exterior.
Recently, secondary batteries are widely used not only for small-sized devices such as cellular phones but also middle-sized or large-sized devices such as vehicles and power storages. When being used for middle-sized or large-sized devices, a great number of secondary batteries are electrically connected to enhance capacity and output. In particular, in middle-sized or large-sized devices, pouch-type secondary batteries are frequently used since they can be easily stacked.
However, a pouch-type secondary battery does not have great mechanical rigidity since it is generally packaged with a battery case made of a laminate sheet of aluminum and polymer. Therefore, when configuring a battery module including a plurality of pouch-type secondary batteries, a stacking frame is frequently used to protect the secondary batteries from external impacts or the like, prevent fluctuation of the secondary batteries and facilitate easier stacking of the secondary batteries. This stacking frame is also called a cartridge.
FIG. 1 is a top view schematically showing an existing frame for a secondary battery.
Referring to FIG. 1, the existing frame for a secondary battery may be configured to have a frame body 10 in a tetragonal plate shape with a hollow center, and a rim of a secondary battery may be placed on a part of the frame body 10. In addition, a plurality of frames may be stacked to configure a battery module, and a secondary battery may be located in a vacuum space formed among the stacked frames.
Meanwhile, when a plurality of secondary batteries are assembled using a plurality of frames as described above, a cooling plate 20 may be interposed between secondary batteries as shown in FIG. 1. The secondary battery may be used in a high-temperature environment, for example in summer, and the secondary battery may also generate heat in itself. At this time, if a plurality of secondary batteries are stacked, the temperature of the secondary batteries may rise higher. If the temperature rises higher than a suitable level, the secondary batteries may suffer from deteriorated performance or in severe cases may cause explosion or fire. Therefore, when configuring a battery module, the cooling plate 20, also called a cooling fin, is frequently interposed between secondary batteries in order to prevent a temperature rise of the secondary batteries by means of the cooling plate 20.
If the cooling plate 20 is interposed between secondary batteries of the battery module, the secondary batteries may be cooled in various forms and ways. Representatively, an external air may be allowed to flow around the cooling plate 20 to lower the temperature of secondary batteries by means of heat exchange between the cooling plate 20 and the air, which is called air-cooling, widely used in the art.
Generally, the cooling plate 20 is made of metallic material such as aluminum, and other portions except for the cooling fin, namely the frame body 10, may be made of plastic or the like. The frame for a secondary battery may be manufactured in various ways, representatively by means of insert injection. In the insert injection, the cooling plate 20 is prepared first, and then, in a state where the cooling plate 20 is put into an insert-injection molding machine, the frame body 10 is injection-molded to make the frame for a secondary battery.
However, in the above manufacturing method, the cooling plate 20 may be deformed due to the shrinkage of the frame body 10. In other words, during the insert-injection molding, a cooling process from high temperature to low temperature is performed, and at this time, the frame body 10 subject to injection molding may be relatively greatly shrunken in comparison to the cooling plate 20. For example, during the cooling process, the frame body 10 may be shrunken as indicated by arrows in FIG. 1.
The cooling plate 20 is commonly configured to have a thin plate shape. Therefore, if the frame body 10 is shrunken as described above, the cooling plate 20 may be deformed or distorted while being impatient to the shrinkage of the frame body 10. In addition, such deformation or distortion may result in the decrease of a contact surface between the secondary battery and the cooling plate 20 or an instable cooling channel, which may greatly deteriorate the cooling effects.
Moreover, if the cooling plate 20 is distorted or deformed due to expansion or shrinkage of the frame body 10, the shape or size of the frame for a secondary battery may vary as a whole. Therefore, when configuring a battery module by stacking such frames for a secondary battery, the frames may not be easily stacked, and also after they are completely stacked, the overall shape or dimension of the battery module may be changed or the frames may be stacked unstably.